The present invention relates to a ribbon device for typewriters or similar office machines of the type including a single-use ribbon disposed in a cassette and moved by a driving device through a printing station while being unwound from a supply reel and wound onto a takeup reel, the device further including a scanning device disposed on a receiving device for the ribbon reels or for the ribbon cassette, respectively, in the machine, for scanning scannable markings disposed at the end of the ribbon, and a control circuit for processing the received signals generated by the scanning device so as to generate a ribbon end signal
U.S. Pat. No. 4,115,013 discloses a ribbon device in which one end of the ribbon is provided with a light reflecting marked surface which is scanned by an optical scanner for processing received signals which actuate a ribbon end signal. Although the ribbon end alarm is here generated without contact, switching reliability will no longer be ensured if the transmitting and/or receiving surfaces of the optical scanner are soiled.
Soiling of the optical scanner may result in the end of the ribbon not being indicated to the machine operator. The consequence of this may be that key strokes repeatedly hit the same place on the ribbon. The production of a clean printed image is interfered with so that the entire typing process must be begun anew.
U.S. Pat. No. 4,212,552 also discloses a scanning device for ribbon end markers, but here, too, no coverage and cleaning of the scanner is disclosed.